The present invention relates to an apparatus for separating solids of different shapes and in particular is directed to an apparatus for separating spherically-shaped solids from irregularly-shaped solids.
When producing spherically-shaped solids it may happen that in addition to the desired spherically-shaped solids irregularly-shaped solids are formed. Furthermore, impacts on the produced spherically-shaped solids, occurring during handling and transport, may cause damage of part of the formed spherically-shaped solids. If a spherical shape of the solids is essential for processing and/or use of the solids, it is important to separate the required spherically-shaped solids with a high efficiency from the irregularly-shaped solids.
In this context, reference can be made to the use of solids as catalyst in the oil industry for the catalytic treatment of hydrocarbons, such as for the catalytic desulphurization and demetallization of petroleum residues. The catalytic treatment of hydrocarbons can be carried out in fixed bed reactors or moving bed reactors. Reactors of these types are internally so constructed that one or more beds of catalyst material can be formed with fluid to be treated passing through these beds. At the lower part of the beds normally screens are arranged being impermeable to the catalyst material. Especially when using large-size reactors, which are operated at high pressures, the catalyst material in the catalyst beds should be able to withstand high compression forces. In view of their high crushing strength, the use of spherically-shaped solids as catalyst in reactor bed operations is preferred. Irregularly-shaped solids of a particular material have a crushing strength which is smaller than the crushing strength of spherically-shaped solids of the same material. A further critical point in catalyst bed reactor operations is the efficiency of the screens for separating treated fluid from the catalyst beds. Pinning of the catalyst particles against the screens, therby plugging the screens, should be prevented as much as possible for enabling an undisturbed separation of the reactor effluent through the screens. Since with spherically-shaped catalyst particles the risk of pinning against screens is much less than when using irregularly-shaped catalyst particles, the reactor bed should preferably contain substantially only spherically-shaped catalyst particles.
When the catalyst material in a catalyst bed reactor has been deactivated to a certain extent the reactor is unloaded and filled with fresh catalyst material. The deactivated material is in the meantime treated to remove the contaminations absorbed or adhered during the fluid treatment in the reactors, so that the material may be re-used as catalyst. During the use in the reactor and the cleaning afterwards of the catalyst material the forces exerted on the catalyst material may result in crushing of part of the material, so that a part of the material will become irregularly-shaped. For the reason explained in the above, this crushed part of the catalyst should be removed prior to re-using the material in reactors.
From the above it will be clear that catalyst used in reactors should preferably be spherically-shaped and irregularly-shaped particles should be removed as much as possible from the bulk of desired spherically-shaped particles.
Apart from the above-mentioned example wherein the use of spherically-shaped particles is essential, there are a large variety of other operations wherein a spherical shape of the applied particles is of great importance.
A further example is amongst others the production of porous products built up from separate particles. To obtain a sufficient porosity of the product the base particles should preferably have a uniform spherical shape.
The ever increasing demand for larger quantities of products, prepared by means of particles of spherical shape, requires separating apparatus for separating spherically-shaped particles from irregularly-shaped particles having a high efficiency and allowing high throughputs.